1899] MICROSCOPICAL JOURNAL. 129 



mercial gelatin of uniform character and washed free from 

 all inhibiting- acid substances is a desideratum. — Bot. Gaz. 



Gram's Method of Double Staining Micro-organisms 

 of all Sorts. — This consists in using )A cc. of a, saturated 

 alcoholic solution of gentain violet and 10 cc. of a solution 

 of anilin-water gentian violet mixed. The resultant dye 

 will be deeply colored and opaque. For the watery solution 

 take alittle anilin oil in a test tube, then add pure water, 

 shake, filter. The filtrate should be clear, not cloudy. A 

 cover-glass containing the smear of any sort is rendered 

 dry by contact with flame and dropped into a saucer 

 cantaining the dye, specimen side down into the liquid 

 where it may remain say four minutes. Holding- the cover 

 glass with forceps wash it thouroughly and immerse it for 

 4 minutes in a solution made of one gram of iodine dis- 

 solved with 2 grains of potassium iodide in 300 cc. of dis- 

 tilled water. Again wash in water and put it in 95 per cent 

 alcohol which will take the stain out of the background but 

 leave the micrococci or bacteria beautifully colored so that 

 they can be readily viewed under one-sixth inch objectives. 

 Prior thereto the cover-glass can be put into dilute eosin 

 for an instant, not exceeding 25 or 30 seconds, which will 

 give a contrast stain the back-ground making the objects 

 stand out still more clearly. Some skill is needed to en- 

 able one to stop the alcoholic decolorization at the point 

 where the background is cleared and before the objects 

 loose their stain for in due time the alcohol would entirely 

 decolor the whole specimen. Likewise avoid too much eosin, 

 else after staining the background it proceeds to mix with 

 and injuire the first stain. The eosin gives light pink 

 color, a beautiful contrast to the violet-colored micro-or- 



ganisms. 



BIOLOGICAL NOTES. 



Chalk. — In the proceedings of the Cotteswood Natural- 

 ists Field Club, XII, 3, 1898, Mr. Chas. Upton writes of 

 the contents of a piece of upper chalk from Purley using 

 the title ''Chalk under the Microscope," 



